The present invention relates to a printing apparatus used for data output in electric data recording devices, for instance, wordprocessor, video tape recorder, electronic still camera and the like.
One example of such a printing apparatus is a laser printer which is well known in optical and electrophotographic fields. Some of the laser printers include a rotary drum rotatably disposed in a printer housing or an endless belt movably supported by a plurality of guide rollers which are disposed in the housing. The rotary drum or endless belt has on a circumferential surface thereof a layer of photosensitive material , for instance organic photo conductor characterized by photoconductivity. The photosensitive material layer on the surface of the rotary drum or endless belt is electrostatically charged and then exposed to a laser beam during the motion of the rotary drum or endless belt. A portion of the photosensitive material layer which is exposed to the laser beam, is electrically discharged. An electrostatic latent image is formed on the layer as a result of the exposure to the laser beam, and then developed by means of toner. The toner-developed image is transferred onto a sheet of recording medium by heating and pressing, and then fixed in such a manner as heating and pressing. Thus, an image corresponding to that of data transmitted to the laser printer is printed onto the sheet of recording medium.
When the photosensitive material layer is deteriorated due to oxidization or damage during its repeated use, the rotary drum or endless belt must be as a whole replaced by a new one. Such a replacement work is inconvenient and particularly, the replacement of the endless belt is complicated.
Further, since the rotary drum or endless belt occupy a relatively large installation space in the conventional printer, other components must be arranged or installed in the remainder small space in the printer.
In addition, one cycle of a printing operation for printing onto one sheet of recording medium in the conventional printer includes the sequential steps of exposure, development, transfer, fixing and the like. The steps are performed in turn but not individually nor simultaneously. Therefore, in such a case that a plurality of sheets of recording medium are printed in the conventional printer, an increased period of time is required therefor.
Furthermore, in order to improve accuracy of the printing operation, the conventional printer employing the endless belt is required to be supplementally provided with a device for preventing offset of the endless belt during travel thereof. The provision of the offset preventing device leads to a complicated structure of the conventional printer.